Phot r 55mm adapter ring is specifically designed to allow the cokin filter holder to attach to lenses with a 55mm filter thread the adapter ring thread allows you to use a minimum number of step up rings otherwise the holder will be pushed away from the lens and vignetting is possible made to fit 55mm lenses and cokin p series filter holdercompatible with most camera lenses includingcanon nikon pentax olympusthe adapter ring thread allows you to use a minimum number of step up rings o